Adaptive Transmission Policies Research Articles

Minimizing Age-of-Information in HARQ-CC Aided NOMA Systems

In this paper, we investigate the timeliness performance of a downlink wireless communication system with non-orthogonal multiple access (NOMA). The timeliness of the system is characterized by Age of Information (AoI). To efficiently utilize the time-frequency resource and achieve a tradeoff between timeliness and reliability, we propose an adaptive transmission policy under hybrid automatic repeat request with chase combining (HARQ-CC) aided NOMA systems. In particular, the BS can adaptively adjust the power allocation and decide whether to transmit old or new packets to users in the NOMA system, based on the current AoI status and the positive/negative acknowledgement (ACK/NACK) feedback signal. We first analyze the BLER under such adaptive systems, and then formulate an AoI minimization problem based on the derived BLER. By transforming the objective function to a Markov Decision Process (MDP) problem, an optimal policy is obtained to minimize the average AoI of the system. Considering the high complexity of the MDP, we further divise an alternative near-optimal policy based on Lyapunov Drift function. Furthermore, we consider the fairness of users and propose a greedy policy to minimize the maximal expected AoI of users. Based on extensive simulations, it has been found that NOMA can outperform OMA on both an overall and a user-level basis when operating with adaptive retransmission and power allocation strategies.

An approximate statistical analysis of wireless channel over α − μ shadowed fading channel

SummaryIn this work, we have comprehensively investigated the impact of non‐linearity (α − μ) and shadowing (inverse gamma) collectively over the wireless channel. To this effect, an approximate closed‐form probability density function (PDF) expression is derived over α − μ/inverse gamma fading channel by employing Gauss–Laguerre quadrature polynomial. The accuracy of the proposed approximate solution is validated through the Kullback–Leibler divergence test. Subsequently, the proposed solution is utilized in the development of various fundamental statistics like commutative distribution function (CDF), moment generating function (MGF) and nth moment. This contribution also includes the derivation of coding gain and diversity gain to study average symbol error probability (SEP) with MRC and EGC diversity. It is observed that diversity gain is independent of shadowing and as the channel condition improves, the coding gain decreases. Finally, the closed‐form solutions of spectral efficiency under different adaptive transmission policies are also developed specifically, optimal power and rate adaptation (OPRA) and effective capacity along with simpler low‐ and high‐power expressions. Monte‐Carlo simulations are utilized to validate the proposed analytical and numerical results.

Uniform thresholding based transmission policy for energy harvesting wireless sensor nodes in fading channel

The work presents a novel computationally efficient transmission policy for throughput maximization over point-to-point sensor links employing harvest-use-store protocol with finite storage capacity battery. In these settings, under finite averaging duration constraint, the stochastic dynamic programming (SDP) technique provides the optimal solution for throughput maximization, but the implementation complexity for SDP is prohibitively large. Thus, there is a need to explore new solutions that can provide near-optimal throughput with lower implementation complexity. The work in this paper presents a adaptive transmission policy based on uniform thresholding that achieves a near-optimal throughput obtainable by SDP. Quantitative comparison with optimal online policies shows that the proposed policy attains performance close to SDP with lower implementation complexity.

Analysis of Asymmetric Dual-Hop Energy Harvesting-Based Wireless Communication Systems in Mixed Fading Environments

This work investigates the performance of a dual-hop energy harvesting-based fixed-gain amplify-and-forward relaying communication system, subject to fading impairments. We consider a source node ( S) communicating with a destination node ( D), either directly or through a fixed distant relay ( R), which harvests energy from its received signals and uses it to amplify and forward the received signals to D. We also consider maximal-ratio combining at D to combine the signals coming from S and R. Both power-splitting and time-switching energy harvesting protocols are investigated. The S - R link is modeled by Nakagami- m fading model, while the R - D and S - D links experience α- μ fading. Closed-form expressions for the statistical properties of the total signal-to-noise ratio are derived, based on which novel closed-form expressions are then derived for the average symbol error rate as well as for the average channel capacity, considering four different adaptive transmission policies. The derived expressions are validated through Monte Carlo simulations.

Reinforcement learning–enabled efficient data gathering in underground wireless sensor networks

Wireless underground sensor networks (WUSNs) consist of sensors that are buried in and communicate through soil medium, while the channel quality of WUSNs is greatly impacted by the underground environment, such as soil moisture and composition. Due to the precipitation and harsh weather, the underground environments change frequently, which make wireless communication in WUSNs much complicated than that in terrestrial over-the-air wireless sensor networks. To achieve reliable and energy-efficient data gathering in dynamic WUSNs, this article proposes an optimal transmission policy, where path loss of sensory data transmission, energy constraint, and network load balancing are the factors to be considered. Specifically, we capture the effect of underground environments on wireless communications, and evaluate path probability, energy consumption, and load balancing factor with respect to reliability and efficiency of transmission paths. The transmission topology can be reduced to a multi-objective and multi-constrained optimization problem and solved through an improved maximum flow minimum cost algorithm. By using reinforcement learning, we derive an adaptive transmission policy for underground sensors to efficiently use their energy and avoid transmitting sensory data in unreliable paths under a dynamic environment. Through simulations and comparison upon publicly available real data, our technique achieves more reliable wireless communication with significant reduction of packet loss, and enables more energy-efficient data gathering than other techniques, especially when soil moisture varies frequently.

Buffer-Aided Secure Relay Networks With SWIPT

In this paper, we propose the use of data and energy buffering in wireless powered relays, while we also design scheduling schemes, with the aim to increase the secrecy throughput. More specifically, it is assumed that Alice transmits information to Bob by using half-duplex randomize-and-forward relaying with simultaneous wireless information and power transfer, under the existence of a passive eavesdropper. First, considering a conventional system, i.e., without energy and data buffering, an optimal baseline policy is designed. Then, focusing on buffer-aided relaying, we maximize the average secrecy throughput under the stability requirement for data and energy queues by using the framework of Lyapunov optimization, according to which, we transform the initial stochastic optimization problem into a sequence of online subproblems. The proposed online adaptive transmission policy dynamically allocates the available resources, i.e., time and power, with respect to the channel state information, as well as the states of the buffers. In addition, our analysis reveals the existence of an interesting trade-off between the average secrecy throughput and the average queue delay. Simulation results validate the analysis and demonstrate that the proposed buffer-aided scheme significantly improves the average secrecy throughput compared to the baseline one.

Unified analysis of channel capacity under different adaptive transmission policies

In this Letter, the channel capacity under different transmission policies is analysed using a mixture gamma distribution. Specifically, the capacity of the channel with inversion and fixed rate, optimum power and rate adaptation, and truncated inversion and fixed rate IS derived in unified exact simple closed-form expressions. The composite α − λ − η − μ /gamma fading channel which includes most of the well-known fading distributions as special cases, has been employed in this work. Moreover, a comparison between numerical and simulation results has been carried out to verify the validation of the derived expressions.

Effective Capacity of $L_p$ -Norm Diversity Receivers Over Generalized Fading Channels Under Adaptive Transmission Schemes

This paper presents novel moment generating function (MGF)- and characteristic function (CHF)-based frameworks for the EC performance analysis of a generic L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -norm diversity combining scheme under adaptive transmission policies. The considered system operates over generalized fading channels, a maximum delay constraint and under various channel state information (CSI) conditions. Depending upon the operational CSI, four policies are studied, namely: i) Constant power with optimal rate adaptation (ORA); ii) Optimal power and rate adaptation (OPRA); iii) Channel inversion with fixed rate (CIFR); and iv) Truncated CIFR (TIFR). The L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -norm diversity is a generic diversity structure which includes as special cases various well-known diversity schemes, such as equal gain combining (EGC), maximal ratio combining (MRC) and amplify-and-forward (AF) relaying. Under the ORA and OPRA policies, we derive single integral expressions for evaluating the EC of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -norm diversity reception directly from the MGF or the incomplete MGF of the Signal-to-Noise-Ratio (SNR) at the receiver, respectively. For the EC performance evaluation of the EGC and AF relaying systems operating under the OPRA policy, a CHF-based approach, which is computationally more efficient as compared to the MGF-based approach, is further presented. It is shown that the EC for the CIFR and TIFR policies can be directly evaluated from the MGF or the CHF of the SNR at the receiver, respectively. For the ORA policy, a novel analytical approach for the asymptotic EC performance analysis is also developed and evaluated, revealing how important system operation parameters affect the overall system performance. The mathematical formalism is validated with selected numerical and equivalent simulation performance evaluation results, thus confirming the correctness of the proposed analytical methodology.

Relay-Assisted Proactive Eavesdropping With Cooperative Jamming and Spoofing

In this paper, we consider a legitimate proactive eavesdropping scenario where a distant central monitor covertly wiretaps the communication between a pair of suspicious users via several multi-antenna full-duplex spoofing relays and a multi-antenna cooperative jammer. Assuming an adaptive transmission policy at the suspicious users, the spoofing relays not only intercept but also forward the manipulated information to control the data rate of the suspicious users in collaboration with the jammer. We provide a technique which jointly optimizes the receive combining vector at the central monitor, the precoders at the relays, and the transmit covariance matrix at the jammer for maximizing the eavesdropping rate. To reveal some fundamental properties of the optimal operation, we first study a single-relay system. It is shown that when the central monitor experiences a poor eavesdropping channel link, the spoofing relay and the jammer should transmit destructive signals and jamming signals, respectively. In this case, the suspicious users are forced to decrease their data rate, while the intercepted information can be successfully decoded by the central monitor. On the other hand, when the eavesdropping channel condition is favorable, the spoofing relay forwards constructive signals to further increase the data rate at the suspicious users in a way that more information can be intercepted from the suspicious users. We then formulate a general eavesdropping rate maximization problem for multiple relays and present a semi-definite relaxation approach. A low-complexity design is also proposed based on our analysis for the single-relay system. Simulation results verify the efficiency of the proposed solutions compared to other baseline schemes in various practical setups.

An analytical study for an efficient multi‐branch switched diversity receiver

SummaryThe development of new hybrid diversity methods has been demanded by the continuous growth of information rates. These schemes achieve improved balance between hardware complexity and performance, in relation to conventional ones. In this paper, a new hybrid switched diversity system is proposed. It is called generalized multi‐branch switch and examine combining. The new scheme is a generalization of the classic one known as switch and examine combining with considerably improved performance. The performance of this scheme is analyzed over independent and identically distributed Nakagami‐m fading channels using well‐known performance and complexity measures. More specifically, important performance metrics, such as the outage probability, the average bit error rate, and the capacity under different adaptive transmission policies, have been analytically studied. It is shown that the proposed approach offers an important improvement on the performance, without considerably affecting the complexity.

Capacity Analysis of $\alpha $ - $\eta $ - $\kappa $ - $\mu $ Fading Channels

The $\alpha $ - $\eta $ - $\kappa $ - $\mu $ model was recently proposed as a generalized fading and can include all well-known small-scale fading models as special cases. In this letter, we investigate the channel capacity of wireless communications that operate in $\alpha $ - $\eta $ - $\kappa $ - $\mu $ fading channels. More specifically, novel and exact expressions for the channel capacity under different adaptive transmission policies are derived in terms of infinite series. Previous results can be obtained through our newly derived expressions by combining and/or specializing the various parameters of the $\alpha $ - $\eta $ - $\kappa $ - $\mu $ model. Moreover, our derived analytical expressions assess the impact of fading parameters on the channel capacity, and are illustrated by simulation results.

Channel Capacity Analysis over Slow Fading Environment: Unified Truncated Moment Generating Function Approach

A unified approach based on truncated moment generating function (TMGF) is employed to derive the explicit expressions for channel capacity of log-normal channel under different adaptive transmission policy. The analysis is carried out assuming channel state information known to both transmitter and receiver. The efficacy of the approach is based on the fact it yields computationally convenient and efficient results in log-normal fading environment. Based on TMGF, a simple closed form expression for higher order moments of channel capacity for log-normal channels is obtained when channel state information is only known to receiver. Numerical computation in relation to simulation results for varying value of $$\sigma _{ dB}$$?dB over permissible range are carried out to validate the accuracy of derived expressions.

Performance of Selection Combining Diversity in &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\eta{-}\mu$&lt;/tex-math&gt;&lt;/inline-formula&gt; Fading Channels With Integer Values of &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\mu$&lt;/tex-math&gt;&lt;/inline-formula&gt;

An analytical study of selection combining (SC) diversity under η-μ multipath fading is presented, considering that the μ parameter takes integer values. Closed-form expressions are derived for the statistics of the signal-to-noise ratio (SNR) at the combiner output and for the error rate of some relevant M-ary modulation schemes. Additionally, closed-form expressions are also derived for the channel capacity, considering different adaptive transmission policies. It is shown that, if the number of receive branches is high enough, severe fading may result in an increased channel capacity for all the considered transmission strategies due to the branch selection and the higher channel variability. This is in sharp contrast to the behavior of capacity in single-channel reception schemes. Monte Carlo simulations have been carried out to validate the derived analytical expressions.

Capacity Analysis of Adaptive Transmission with Space–Time Block Codes in Spatially Correlated MIMO Nakagami- $$m$$ m Fading Channels

In this paper we investigate the impacts of spatial fading correlation on channel capacity of orthogonal space---time block codes (STBCs) over multiple-input multiple-output Nakagami- $$m$$ m fading under different power and rate allocation policy. This paper presents the single-input single-output equivalency of STBC which is equivalent to scalar additive white Gaussian noise channel, with a channel gain proportional to the Frobenius norm of the matrix channel. We derive the characteristic function (c.f.) of the signal-to-noise ratio at the output of the STBC decoder, when spatial fading correlation is assumed. The c.f. turns out to be a linear combination of Laplace transforms weighted by the eigenvalues of the channel correlation matrix, where each element corresponds to an elementary Gamma probability density function. Based on this approach, and using the linearity of the Laplace transform, the capacity expressions are derived for STBC under different adaptive transmission policy. Numerical results illustrate the impact of fading correlation and fading severity on the channel capacity and outline the performance differences between the distinctive adaptation policies.

System performance of Rayleigh fading channel in the presence of adjacent channel interference

In this paper, the authors study the system performance of adaptive transmission techniques in the presence of adjacent channel interference (ACI). The authors obtain closed-form expressions for system capacity when employing different adaptive transmission policies with and without diversity schemes. The simulation results of spectrum efficiency in a WiMAX network employing 256 orthogonal frequency division multiplexing subcarriers are obtained for the analytical expressions derived for selection combining diversity under various adaptation policies. Analytical results show that the optimal power and rate adaptation policy provides the highest spectrum efficiency. Both analytical and simulation results are found to be in close agreement with each other, which shows that the obtained analytical results works well with the scenario of ACI. Also, maximal ratio combining scheme yields the highest spectrum efficiency when subjected to ACI.

Dual-Hop Optical Wireless Relaying Over Turbulence Channels With Pointing Error Impairments

In this paper, we present analytical expressions for the performance of dual-hop urban optical wireless communication system under the combined influence of atmospheric turbulence induced-fading and misalignment-fading (pointing errors). The system employs an amplify and forward relay with the assumption that channel state information is available at transmitting as well as receiving terminals. The atmospheric turbulence channels are modeled by independent but not necessarily identically distributed (i.n.i.d) Gamma-Gamma fading statistics with pointing error impairments. Using a tight upper bound for the end-to-end signal to noise ratio of the system, we derive the novel closed form expressions for the moment generating function and probability density function all in terms of Meijer's G-function. Based on the aforementioned statistical results, accurate closed-form expressions for average symbol error rate for M-ary phase shift keying modulation schemes, outage probability and the ergodic capacity under four adaptive transmission policies namely optimal rate adaptation, optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate are derived in terms of Meijer's G -function function. Finally, the proposed mathematical analysis is accompanied with various numerical examples to demonstrate the effect of different system parameters on the system performance.

Adaptive transmission policy over Rayleigh fading channels for cooperative networks with limited feedback

The authors propose an adaptive transmission scheme for cooperative communication networks. The cooperative network with the proposed scheme chooses the transmission rate and decides to involve the relay in transmission, adapting to the channel state estimated from limited feedback information (e.g. positive/negative acknowledgement (ACK/NACK) feedback). Considering that the limited feedback information provides only partial knowledge about the actual channel states, the authors design a decision-making algorithm on cooperative transmission by using a partially observable Markov decision process framework. The simulation results show that, when the feedback overhead is taken into account, the proposed scheme outperforms even the scheme with which the states of all relevant channels are estimated and fed back.

Cross-Layer Optimization of Two-Way Relaying for Statistical QoS Guarantees

Two-way relaying promises considerable improvements on spectral efficiency in wireless relay networks. While most existing works focus on physical layer approaches to exploit its capacity gain, the benefits of two-way relaying on upper layers are much less investigated. In this paper, we study the cross-layer design and optimization for delay quality-of-service (QoS) provisioning in two-way relay systems. Our goal is to find the optimal transmission policy to maximize the weighted sum throughput of the two users in the physical layer while guaranteeing the individual statistical delay-QoS requirement for each user in the datalink layer. This statistical delay-QoS requirement is characterized by the QoS exponent. By integrating the concept of effective capacity, the cross-layer optimization problem is equivalent to a weighted sum effective capacity maximization problem. We derive the jointly optimal power and rate adaptation policies for both three-phase and two-phase two-way relay protocols. Numerical results show that the proposed adaptive transmission policies can efficiently provide QoS guarantees and improve the performance. In addition, the throughput gain obtained by the considered three-phase and two-phase protocols over direct transmission is significant when the delay-QoS requirements are loose, but the gain diminishes at tight delay requirements. It is also found that, in the two-phase protocol, the relay node should be placed closer to the source with more stringent delay requirement.

Spectrum Efficiency of WiMAX Networks in the presence of Interference with Diversity Combining

Worldwide Interoperability for Microwave Access) is a promising technology which can offer high speed voice, video and data services upto the requirements at the customer's end. The objectives of this paper is to evaluate the Performance evaluation of a WiMAX system under various diversity schemes (Selection combining, Maximal ratio combining and Equal gain combining), employing different adaptive transmission policies, such as Optimal power and rate adaptation policy, Optimal rate adaptation with constant transmit power policy, Channel inversion with fixed rate policy, and Truncated channel inversion policy, subjected to co-channel interference and adjacent channel interference. WiMAX system incorporates OFDM with 256 sub-carriers with QPSK modulation as the transmission scheme. Simulated results of the estimated spectrum efficiency show that the implementation of Optimal power and rate adaptation policy under Selection combining is highly effective to combat co- channel interference and adjacent channel interference in the WiMAX communication system. Keywords-channel interference; Adjacent channel interference; Optimal power and rate adaptation policy; Optimal rate adaptation with constant transmit power policy; Channel inversion with fixed rate policy; Truncated channel inversion with fixed rate policy.

Spectrum efficiency of Fixed WiMAX OFDM network in the presence of co-channel interference with diversity combining

WiMAX (Worldwide Interoperability for Microwave Access) is a promising technology which can offer high speed voice, video and data services upto the requirements at the customer's end. The objectives of this paper is the Performance evaluation of a WiMAX system under various diversity schemes (Selection combining, Maximal ratio combining and Equal gain combining), employing different adaptive transmission policies, such as Optimal power and rate adaptation policy, Optimal rate adaptation with constant transmit power policy, Channel inversion with fixed rate policy, and Truncated channel inversion policy, subjected to co-channel interference. The WiMAX system incorporates OFDM with BPSK modulation as the transmission scheme. Simulated results of the estimated spectrum efficiency shows that the implementation of Optimal power and rate adaptation policy is highly effective to combat co-channel interference in the WiMAX communication system, under Selection combining.